Biometric authentication device, biometric authentication method, and computer readable, non-transitory medium

ABSTRACT

A biometric authentication device includes: a first biometric sensor that obtains biometric information of a user; a second biometric sensor that obtains biometric information of a user at a lower degree of reproducibility than the first biometric sensor; an authentication process unit that performs an authentication by comparing with use of the biometric information obtained by the first biometric sensor and the second biometric sensor, wherein the authentication process unit compares biometric information obtained by the second biometric sensor with use of biometric information obtained by the first biometric sensor of a case where a comparing between the biometric information obtained by the first biometric sensor and enrolled information is successful.

This application is a continuation application of InternationalApplication PCT/JP2012/058169 filed on Mar. 28, 2012 and designated theU.S., the entire contents of which are incorporated herein by reference.

FIELD

A certain aspect of the embodiments is related to a biometricauthentication device, a biometric authentication method and acomputer-readable, non-transitory medium.

BACKGROUND

A biometric authentication is performed by comparing a comparison-usedata obtained by a biometric sensor and an enrolled data enrolled in adatabase. Recently, the biometric authentication is diversified. PatentDocuments 1 to 3 disclose a technology of the diversified biometricauthentications.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Laid-open Patent Publication No. 2001-14462

Patent Document 2: Japanese Laid-open Patent Publication No. 2006-107340

Patent Document 3: Japanese Laid-open Patent Publication No. 2009-169796

SUMMARY

According to an aspect of the present invention, there is provided abiometric authentication device including: a first biometric sensor thatobtains biometric information of a user; a second biometric sensor thatobtains biometric information of a user at a lower degree ofreproducibility than the first biometric sensor; an authenticationprocess unit that performs an authentication by comparing with use ofthe biometric information obtained by the first biometric sensor and thesecond biometric sensor, wherein the authentication process unitcompares biometric information obtained by the second biometric sensorwith use of biometric information obtained by the first biometric sensorof a case where a comparing between the biometric information obtainedby the first biometric sensor and enrolled information is successful.

According to an aspect of the present invention, there is provided abiometric authentication method including: performing an authenticationby comparing biometric information obtained by a first biometric sensorthat obtains biometric information of a user and an enrolledinformation; and with use of the biometric information of a case wherethe comparing is successful, performing an authentication by comparingbiometric information obtained by a second biometric sensor that obtainsbiometric information of a user at a lower degree of reproducibilitythan the first biometric sensor.

According to an aspect of the present invention, there is provided acomputer readable, non-transitory medium storing a program that causes acomputer to execute a process, the process including: performing anauthentication by comparing biometric information obtained by a firstbiometric sensor that obtains biometric information of a user and anenrolled information; and with use of the biometric information of acase where the comparing is successful, performing an authentication bycomparing biometric information obtained by a second biometric sensorthat obtains biometric information of a user at a lower degree ofreproducibility than the first biometric sensor.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing for describing a situation example where embodimentsare applied;

FIG. 2A illustrates a block diagram for describing a hardware structureof a biometric authentication device in accordance with a firstembodiment;

FIG. 2B illustrates a schematic view for describing an example of abiometric sensor to detect a palm vein;

FIG. 3A illustrates a block diagram of each function realized by anexecution of a biometric authentication program;

FIG. 3B illustrates a table example showing an enrolled templateenrolled in an enrollment database;

FIG. 4 illustrates an example of a flowchart executed during anauthentication process with use of at biometric sensor;

FIG. 5 illustrates an example of generation of an image having low imagequality.

FIG. 6 illustrates another example of generation of an image having lowimage quality;

FIG. 7 illustrates another example of generation of an image having lowimage quality;

FIG. 8 illustrates an example of a flowchart executed during anauthentication process with use of a biometric sensor;

FIG. 9 illustrates an example of a process flow for estimating a factorof a failure of an authentication;

FIG. 10 illustrates influence of hand size on limb darkening.

FIG. 11 illustrates a fusion score;

FIG. 12 illustrates a block diagram for describing a hardware structureof a biometric authentication device in accordance with a secondembodiment;

FIG. 13 illustrates a block diagram of each function realized by anexecution of a biometric authentication program;

FIG. 14 illustrates an example of a flowchart executed during anauthentication process with use of a biometric sensor;

FIG. 15 illustrates an example of a flowchart executed during anauthentication process with use of a second biometric sensor; and

FIG. 16 illustrates an example of a flowchart executed by a server aftera Step S53 of FIG. 15.

DESCRIPTION OF EMBODIMENTS

A description will be given of a situation example where the followingembodiments are applied, before describing the embodiments. FIG. 1 is adrawing for describing the situation example where the followingembodiments are applied. With reference to FIG. 1, a sensor foradministration of entering or leaving a room (type A sensor) and asensor for administration of log-on of a PC in an office, administrationof door lock or the like (type B sensor) are provided. A biometricauthentication is performed by comparing biometric information obtainedby a biometric sensor and enrolled information enrolled in an enrollmentdatabase.

The administration of entering or leaving a room is a first stage of asecurity. Therefore, high accuracy authentication is required for thetype A sensor. And so, a sensor that has high authentication accuracyand high resistance against outer light but is large and expensive isused as the type A sensor. On the other hand, a sensor used in eachdesktop PC or note PC in an office has a limit in size. The number ofthe PCs is large. Therefore, cost cut is required. And so, a small andinexpensive sensor is used as the type B sensor. In this case,authentication accuracy in the office is degraded. It is demanded thatthe authentication accuracy of the type B sensor is improved. And so, inthe following embodiments, a description will be given of a biometricauthentication device, a biometric authentication method and a biometricauthentication program that are capable of suppressing degradation ofauthentication accuracy in a case where a plurality of sensors are used.

First Embodiment

FIG. 2A illustrates a block diagram for describing a hardware structureof a biometric authentication device 400 in accordance with a firstembodiment. With reference to FIG. 2A, the biometric authenticationdevice 400 has a structure in which a terminal 100, a terminal 200 and astorage device 300 are coupled with each other via a network. Acommunication network such as an intranet, a public line network orinternet may be used as the network. For example, the terminal 100 is adevice to determine allowing of entering an office. The terminal 100 isa PC terminal provided in the office.

The terminal 100 has a CPU 101, a RAM 102, a storage device 103, a firstbiometric sensor 104, a display device 105, a communication device 106and so on. These components are coupled with each other via a bus or thelike. The terminal 200 has a CPU 201, a RAM 202, a storage device 203, asecond biometric sensor 204, a display device 205, a communicationdevice 206 and so on. These components are coupled with each other via abus or the like.

The CPUs (Central Processing Unit) 101 and 201 are central processingunits. The CPUs 101 and 201 include one or more core. The RAM (RandomAccess Memory) 102 is a volatile memory temporally storing a programexecuted by the CPU 101, a data processed by the CPU 101, and so on. TheRAM 202 is a volatile memory temporally storing a program executed bythe CPU 201, a data processed by the CPU 201, and so on.

The storage devices 103 and 203 are nonvolatile memory devices. Thestorage devices 103 and 203 may be SSDs (Solid State Drive) such as ROMs(Read Only Memory) or flash memories, or hard disks driven by hard diskdrives. The display device 105 is a device for showing a result of eachprocess of the terminal 100. The display device 205 is a device forshowing a result of each process of the terminal 200. The displaydevices 105 and 205 are liquid crystal displays or the like. Thecommunication devices 106 and 206 are interfaces for transmitting andreceiving a signal with an outer component.

The first biometric sensor 104 and the second biometric sensor 204 aresensors to obtain biometric information of a user. The biometricinformation of a user is not limited, and is information of a biometricbody such as a fingerprint, a vein, an iris, a voiceprint or a shape. Inthe embodiment, a sensor to detect an image of a palm vein is used asthe first biometric sensor 104 and the second biometric sensor 204, asan example. FIG. 2B illustrates a schematic view for describing thefirst biometric sensor 104 to detect a palm vein.

The first biometric sensor 104 is an imaging device to take an image ofa vein under a palm skin with use of a near-infrared ray having highpermeability with respect to a human body. The first biometric sensor104 has a CMOS (Complementary Metal Oxide Semiconductor) camera or thelike. An illumination to radiate a light including a near-infrared raymay be provided. The second biometric sensor 204 has the same structureas the first biometric sensor 104.

The first biometric sensor 104 has higher reproducibility than thesecond biometric sensor 204 with respect to obtaining biometricinformation of a user. That is, a similarity among biometric informationobtained by the first biometric sensor 104 two or more times is higherthan a similarity among biometric information obtained by the secondbiometric sensor 204 two or more times. When the first biometric sensor104 and the second biometric sensor 204 are sensors to obtain abiometric image, the first biometric sensor 104 has a device structureto achieve higher image quality than the second biometric sensor 204.

A description will be given of high image quality and low image quality.In the embodiment, image quality satisfying the following requirementsis referred to as high image quality. Image quality not satisfying thefollowing requirements is referred to as low image quality. In concrete,image quality having less noise may be referred to as high imagequality. When there is less noise, it is possible to stably extract anauthentication feature and authentication accuracy gets higher. A noiseof an image is determined by light amount of a light source orperformance of a lens. For example, when the light amount is large, thenoise decreases. F value that is an index indicating brightness may beused as the performance of a lens.

Image quality of which limb darkening is small may be referred to ashigh image quality. This is because when the limb darkening is small,feature of an edge of a taken image can be extracted stably. And,authentication accuracy is improved because cut-out process of a portionfor authentication is stabilized. The cut-out process is, for example, aprocess of cutting out a palm region that is an authentication objectfrom an image. The limb darkening is determined by characteristic of alens, evenness of illuminations and so on.

Image quality of which resolution is high may be referred to as highimage quality. This is because when a resolution of an image is high, animage of a fine feature can be taken and the authentication accuracy isimproved. Resolution of an image is determined by a performance of animaging element (CMOS or CCD), a performance of transmission path (forexample, forwarding performance of USB) and so on. With respect to theperformance of transmission path, this is because when capacity of atransmission path is small, it is difficult to actually use thetransmission path because a high resolution data generally has a largedata capacity even if the high resolution data can be obtained with useof an imaging element.

Image quality having high resolving power may be referred to as highimage quality. The resolving power is an index indicatingdistinguishability of small information and is, for example, an index ofdetermining whether a fine line pair is correctly identified as a linepair when an image of a white line and a black line is taken. Inconcrete, when the resolving power is low, the white and the black aremixed, and appear in gray. The resolving power is determined by aperformance of a lens together with the resolution. The MTF (ModulationTransfer Function) may be used as the index of the resolving power.

Image quality having less surface reflection may be referred to as highimage quality. This is because when an amount of the surface reflectionis small, it is possible to clearly take an image of a vein image thatis an inner feature and the authentication accuracy is improved. Asurface reflection component is a reflection component occurring at aninterface between a palm and air. The surface reflection can be reducedwhen a polarization board is mounted. The surface reflection can bereduced by an arrangement of a light source and an illuminating method.

The storage device 300 is a nonvolatile memory device. The storagedevice 300 may be an SSD (Solid State Drive) such as a ROM (Read OnlyMemory) or a flash memory, or a hard disk driven by a hard disk drive. Abiometric authentication program is stored in the storage device 300.The biometric authentication program may be divided into and stored bythe storage devices 103 and 203.

Next, a description will be given of each process of the terminal 100.The biometric authentication program stored in the storage device 300 isdeveloped to the RAMs 102 and 202. The CPU 101 executes the biometricauthentication program developed to the RAM 102. The CPU 201 executesthe biometric authentication program developed to the RAM 202. Thus,each process of the terminal 100 is performed.

FIG. 3A illustrates a block diagram of each function realized by theexecution of the biometric authentication program. With reference toFIG. 3A, by the execution of the biometric authentication program, theterminal 100 acts as an overall control unit 11, an imaging process unit12, an authentication process unit 13, a template obtain unit 14, atemporal template generation unit 15 and an image process unit 16. Bythe execution of the biometric authentication program, the terminal 200acts as an overall control unit 21, an imaging process unit 22, anauthentication process unit 23, a template obtain unit 24 and a templatecash unit 25. And, by the execution of the biometric authenticationprogram, the storage device 300 acts as an enrollment database 30.

The overall control unit 11 controls the imaging process unit 12, theauthentication process unit 13, the template obtain unit 14, thetemporal template generation unit 15 and the image process unit 16. Theimaging process unit 12 obtains a palm image from the first biometricsensor 104 in accordance with an instruction of the overall control unit11. The authentication process unit 13 extracts palm vein informationfrom the palm image obtained by the imaging process unit 12 as anauthentication feature in accordance with an instruction of the overallcontrol unit 11, and performs an authentication process. The templateobtain unit 14 obtains an enrolled template (enrolled data) from theenrollment database 30 for authentication of the authentication processunit 13. The temporal template generation unit 15 generates a temporaltemplate from the authentication feature extracted by the authenticationprocess unit 13. The image process unit 16 processes the image obtainedby the imaging process unit 12.

The overall control unit 21 controls the imaging process unit 22, theauthentication process unit 23, the template obtain unit 24 and thetemplate cash unit 25. The imaging process unit 22 obtains a palm imagefrom the second biometric sensor 204 in accordance with an instructionof the overall control unit 21. The authentication process unit 23extracts palm vein information from the palm image obtained by theimaging process unit 22 as an authentication feature in accordance withan instruction of the overall control unit 21, and performs anauthentication process. The template obtain unit 24 obtains an enrolledtemplate (enrolled data) from the enrollment database 30 forauthentication of the authentication process unit 23. The template cashunit 25 temporarily stores a temporal template generated by the temporaltemplate generation unit 15.

FIG. 3B illustrates a table example showing an enrolled templateenrolled in the enrollment database 30. With reference to FIG. 3B, theenrolled template includes an authentication feature related to an ID ofeach user. The enrolled template may be enrolled in the enrollmentdatabase 30 in advance with use of the first biometric sensor 104. Adescription will be given of details of the authentication process.

[Authentication Process]

FIG. 4 illustrates an example of a flowchart executed during theauthentication process with use of the first biometric sensor 104. Forexample, the authentication process is executed during entering anoffice. The imaging process unit 12 obtains an authentication-use palmimage I from the first biometric sensor 104 (Step S1). Next, theauthentication process unit 13 extracts an authentication feature F fromthe palm image I (Step S2). Next, the authentication process unit 13compares between the authentication feature F and an enrolled templateTR which the template obtain unit 14 obtains from the enrollmentdatabase 30, and calculates a similarity S of the both (Step S3). Theauthentication process unit 13 calculates a similarity between enrolledtemplates (TR1 to TRN) of each user and the authentication feature F.

Next, the authentication process unit 13 determines whether a similarityS of one of users is equal to or more than a threshold TH0 (Step S4).When it is determined as “Yes” in the Step S4, the authenticationprocess unit 13 outputs a signal indicating that the authentication issuccessful (Step S5). Thus, for example, a door for entering the officeis opened. Next, the image process unit 16 generates an image I′ havinglower image quality than the image I by processing the palm image Iallowing the success of the authentication (Step S6).

Here, a description will be given of an example of the generation of theimage I′ having low image quality. For example, when the secondbiometric sensor 204 of which reproducibility is low is used, there maybe case where a sufficient illumination amount is not achieved. Forexample, when the second biometric sensor 204 is built in the note PC,it is necessary to reduce light amount in view of power consumption. Asa result of the reduction of the light amount, many noises are includedin an image. There may be a case where an imaging element (CCD or CMOS)used for obtaining an image is downsized. When an area of the imagingelement is small, a light amount per a unit area is reduced. Thisresults in increase of the noise. A small imaging element is often usedin a small and inexpensive sensor. As a result, the noise tends toincrease.

When the noise is included in the image, extraction of a feature amount(a ridge line of a fingerprint or a vein pattern) is unstable. And so,the image process unit 16 may add a noise to an image obtained by thefirst biometric sensor 104 in order to reduce a difference between imagequality of the image obtained by the first biometric sensor 104 andimage quality of an image obtained by the second biometric sensor 204.For example, the image process unit 16 measures an amount σ of a noiseindicating a difference between the sensors in advance, and adds arandom noise determined based on the σ to pixels of the palm image I. Inconcrete, the image process unit 16 obtains an image I′ in accordancewith the following formula (1). In the following formula (1), I′(x) isthe image I′ after the process. I(x) is the palm image I before theprocess. N(x) is a noise (average=0).

I′(x)=I(x)+N(x)  (1)

FIG. 5 illustrates another example of the generation of the image I′having low image quality. For example, when a small sensor is used asthe second biometric sensor 204, a sensor area is small. Therefore,there may be a case where a radiation area of a light source is limited.When the sensor area is small, it is difficult to evenly radiate a lightto a subject such as a palm. In this case, when limb darkening is addedto an image obtained by the first biometric sensor 104, a differencebetween image quality of the image obtained by the first biometricsensor 104 and image quality of an image obtained by the secondbiometric sensor 204 can be reduced. For example, with reference to FIG.5, the image process unit 16 obtains a limb darkening conversion curveindicating a difference between distribution of luminance values of theimage obtained by the first biometric sensor 104 and distribution ofluminance values of the image obtained by the second biometric sensor204 in advance. Further, the image process unit 16 generates the imageI′ having low image quality by applying the limb darkening curve to theimage obtained by the first biometric sensor 104. Thus, the differencebetween the image quality of the image obtained by the first biometricsensor 104 and the image quality of the image obtained by the secondbiometric sensor 204 is reduced. In concrete, the image process unit 16obtains the image I′ in accordance with the following formula (2). Inthe following formula (2), I′(x) is the image I′ after the process. I(x)is the palm image I before the process. a(x) is a limb darkening curve(a(0)=1.0)

I′(x)=a(x)·I(x)  (2)

FIG. 6 illustrates another example of the generation of the image I′having low image quality. For example, when an inexpensive sensor isused as the second biometric sensor 204, the number of lenses, thethickness of the lenses are limited. Optical characteristic is degradedaccording to a material of the lenses. In this case, a sharpness degree(frequency) of the image obtained by the second biometric sensor 204 isdegraded. The sharpness degree can be expressed with use of MTF value.The MTF value is a value in which degradation degree of an originalimage caused by a lens is expressed by a frequency region. In this case,when the frequency characteristic of the image obtained by the firstbiometric sensor 104 is degraded, the difference between the imagequality of the image obtained by the first biometric sensor 104 and theimage quality of the image obtained by the second biometric sensor 204can be reduced. In concrete, with reference to FIG. 6, the image processunit 16 obtains a “frequency degradation curve” matching frequencycharacteristics of sensors in advance, and changes the frequencycharacteristics in accordance with the frequency degradation curve. Inconcrete, the image process unit 16 obtains the image I′ in accordancewith the following formula (3). In the following formula (3), F′(f) isFourier transform of the image I′ after the process. F(f) is Fouriertransform of the palm image I before the process. a(f) is the frequencydegradation curve.

F′(f)=a(f)·F(f)  (3)

A distortion of a lens may be used as an image process for reducing thedifference between lenses. In this case, when the image process unit 16adds a lens distortion to the palm image I obtained by the firstbiometric sensor 104, the difference between the image quality of theimage obtained by the first biometric sensor 104 and the image qualityof the image obtained by the second biometric sensor 204 can be reduced.

FIG. 7 illustrates another example of the generation of the image I′having low image quality. For example, when a high frequency noise isadded to a region of the palm image obtained by the second biometricsensor 204 in which luminance values are high, the difference betweenthe image quality of the image obtained by the first biometric sensor104 and the image quality of the image obtained by the second biometricsensor 204 can be reduced. Surface reflection is likely to occur in aconvex region of a palm with reference to FIG. 7 because an incidentangle is equal to a reflection angle. In the region, an averageluminance value is high. It is therefore possible to predict theoccurrence of the surface reflection with use of the luminance value asa reference. In the region with the surface reflection, a noise of highfrequency occurs because of wrinkles of a surface. Therefore, the imageprocess unit 16 may perform a process of adding a high frequency noiseto the region.

With reference to FIG. 4 again, the authentication process unit 13extracts an authentication feature from the image I′, and the temporaltemplate generation unit 15 transmits the authentication feature to thetemplate cash unit 25 as a temporal template TI′ (Step S7). When it isdetermined as “No” in the Step S4, the authentication process unit 13outputs a signal indicating that the authentication is failed (Step S8).After the Step S7 or the Step S8, the flowchart of FIG. 4 is terminated.

FIG. 8 illustrates an example of a flowchart executed during anauthentication process with use of the second biometric sensor 204. Theauthentication process is performed after the authentication with use ofthe first biometric sensor 104 is successful, and is, for example,performed during a BIOS authentication at a PC starting, a log-onauthentication of an OS, or the like after entering an office. Theimaging process unit 22 obtains an authentication-use palm image I fromthe second biometric sensor 204 (Step S11). Next, the authenticationprocess unit 23 extracts an authentication feature F from the palm imageI (Step S12). Next, the authentication process unit 23 compares betweenthe authentication feature F and an enrolled templates T_(R) which thetemplate obtain unit 24 obtains from the enrollment database 30, andcalculates a similarity S of the both (Step S13).

Next, the authentication process unit 23 determines whether thesimilarity S is equal to or more than a threshold TH₁ (Step S14). Whenit is determined as “No” in the Step S14, the authentication processunit 23 determines whether the similarity S is equal to or more than athreshold TH₂ (<TH₁) (Step S15). When it is determined as “Yes” in theStep S15, the template obtain unit 24 obtains a temporal template T₁from the template cash unit 5 (Step S16).

Next, the authentication process unit 23 compares the authenticationfeature F and the temporal template T_(I′) and calculates a similarityS′ of the both (Step S17). Next, the authentication process unit 23determines whether the similarity S′ is equal to or more than athreshold TH₃ (Step S18). When it is determined as “Yes” in the Step S18or it is determined as “Yes” in the Step S14, the authentication processunit 23 outputs a signal indicating that the authentication issuccessful (Step S19). When it is determined as “No” in the Step S18 orit is determined as “No” in the Step S15, the authentication processunit 23 outputs a signal indicating that the authentication is failed(Step S20). After the Step S19 or the Step S20, the execution of theflowchart of FIG. 8 is terminated.

In the embodiment, it is possible to use biometric information allowingsuccessful of an authentication obtained by the first biometric sensor104 of which reproducibility is high during an authentication based onbiometric information obtained by the second biometric sensor 204 ofwhich reproducibility is low. Therefore, biometric information havinghigh reliability can be used. Accordingly, it is possible to suppressdegradation of authentication accuracy with use of the second biometricsensor 204. And, degradation of convenience may be suppressed. Highreproducibility is not required for the second biometric sensor 204because the biometric information having high reliability can be used.Therefore, an inexpensive device can be used as the second biometricsensor 204. And, the cost can be suppressed.

When a plurality of biometric sensors are provided, there may be a casewhere an enrolled templates is needed for each of the biometric sensors.This is because influence on the authentication accuracy is largebecause a sensor having low image quality is largely subjected toinfluence of a slight posture changing of a subject (palm or the like).In contrast, in the embodiment, it is possible to use a temporaltemplate based on biometric information allowing successful of theauthentication. Therefore, it is not necessary to individually make anenrolled template with respect to each biometric sensor. Accordingly, anamount of the enrolled templates can be reduced.

In the embodiment, it is possible to estimate a factor of a failure ofan authentication by the second biometric sensor 204. In concrete, whenan image having high image quality obtained by the first biometricsensor 104 is used, a factor of the failure of authentication can beestimated. First, there may be a case where time passes from theenrollment of the enrolled template T_(R) in the enrollment database 30to an actual authentication process. In this case, (1) changing ofbiometric body itself, (2) changing unique to a comparing such aschanging of a posture or a noise, and so on are factors of the failureof authentication. Influence of a wound of a surface or the like may bea factor of (1). On the other hand, the factor of (1) is hardly includedin a high image quality image obtained on the day. Therefore, it ispossible to predict a factor of a failure of authentication by comparinga high image quality image obtained by the first biometric sensor 104 onthe day (or in a very short time interval) and an image obtained by thesecond biometric sensor 204.

FIG. 9 illustrates an example of a process flow for estimating a factorof a failure of authentication. With reference to FIG. 9, the imagingprocess unit 22 obtains an authentication-use palm image I from thesecond biometric sensor 204 (Step S21). Next, the authentication processunit 23 compares the authentication feature F extracted from the palmimage I and an enrolled template T_(R) which the template obtain unit 24obtains from the enrollment database 30 and calculates a similarity S₀of the both (Step S22).

Next, the authentication process unit 23 determines whether thesimilarity S₀ is equal to or more than the threshold TH₀ (Step S23).When it is determined as “Yes” in the Step S23, the authenticationprocess unit 23 outputs a signal indicating that the authentication issuccessful (Step S24). When it is determined as “No” in the Step S23,the template obtain unit 24 obtains a temporal template TI′ from thetemplate cash unit 25 (Step S25).

Next, the authentication process unit 23 compares between theauthentication feature F and the temporal template T_(I′) and calculatesa similarity S_(T) of the both (Step S26). Next, the authenticationprocess unit 23 determines whether the similarity S_(T) is equal to ormore than a threshold TH_(T) (Step S27). When it is determined as “Yes”in the Step S27, the authentication process unit 23 estimates that achanging of a biometric body is an error factor and makes the displaydevice 205 show the estimation (Step S28). When it is determined as “No”in the Step S27, the authentication process unit 23 estimates that aposture of the biometric body or the like during the authentication isthe failure of authentication and makes the display device 205 show theestimation (Step S29).

In accordance with the flowchart of FIG. 9, when the authentication withuse of the second biometric sensor 204 is failed, a comparing betweenthe authentication feature F and the temporal template T_(I′) isperformed. When similarity of this case is high, it is estimated that achanging occurs in a biometric feature, because although similaritybetween the temporal template T_(I′) and the authentication feature F ishigh, similarity between an enrolled template enrolled previously andthe authentication feature F is low. In this case, a correctdetermination can be performed by performing an image process forreducing the difference between image qualities of sensors.

Another Example

In the above-mentioned embodiments, the structure in which a temporaltemplate is generated with respect to all users is described. However,the structure is not limited. For example, the generation of thetemporal templates may be valid or invalid with respect to each user.For example, with reference to FIG. 10, the limb darkening has largeinfluence on a person having a large hand but the limb darkening haslittle influence on a person having a small hand. Therefore, when thegeneration of the temporal template is suppressed with respect to theuser having a small hand, the imaging process achieves an effect ofreducing CPU burden, reducing power consumption and reducing storagecapacity.

Influence degree of surface reflection differs with respect to anindividual. This is because a shape of a palm differs with respect to anindividual although the surface reflection is largely subjected toinfluence of an incident angle and a reflection angle of a light.Therefore, there is a user that is largely subjected to influence of thesurface reflection and a user that is not largely subjected to theinfluence of the surface reflection. When a process of adding surfacereflection is applied to a specific user who is largely subjected to thesurface reflection, the above-mentioned effect is achieved.

In the case of the surface reflection, it is difficult to determine withor without applying during enrollment, being different from a size of ahand. This is because, the influence of the surface reflection dependson a holding condition of a palm and it is difficult to determine onlyfrom image data of few times during an enrolling. And so, with orwithout applying may be determined according to a history of theauthentication result. That is, a rate of a failure of authenticationfor a given time or a given times may be searched. When the rate of thefailure of authentication is more than a predetermined value, imagequality of an image of a case where an authentication with use of thebiometric sensor 104 is successful may be degraded and a temporaltemplate may be generated.

In the above-mentioned embodiments, the cases in which an image that isobtained by the first biometric sensor 104 and is processed is used foran authentication with use of the second biometric sensor 204 aredescried. However, the embodiments are not limited. For example, afusion score (total similarity) in which a similarity S_(R) between anauthentication feature F extracted from an image I obtained by thesecond biometric sensor 204 and an enrolled template T_(R) and asimilarity S_(T) between the authentication feature F and the temporaltemplate T_(I′) are combined may be used. For example, a totalsimilarity S_(TOTAL) may be calculated in accordance with the followingformula (4).

S _(TOTAL)=(1.0−w)S _(R) +wS _(T)  (4)

In the above formula (4), “w” is a coefficient indicating a weight ofeach similarity. Just after enrollment of an enrolled template T_(R), adifference between the enrolled template T_(R) and the temporal templateT_(I′) is small. On the other hand, as time passes, the differencebetween the enrolled template T_(R) and the temporal template T_(I′)gets larger. Therefore, “w” may be small just after the enrollment, and“w” may be enlarged as time passes. In the example of FIG. 11, an upperlimit value (0.5) is set in the “w”.

The number of type of a biometric sensor having low reproducibility isnot always one. For example, there may be a case where a plurality ofbiometric sensors having low image quality are provided. For example, itis assumed that a biometric sensor 204 a and a biometric sensor 204 bare provided. In this case, a plurality of factors are mixed as adegradation factor of image quality. For example, it is possible thatreduction of MTF is a degradation factor of the biometric sensor 204 a,and reduction of MTF and a noise are two degradation factors of thesecond biometric sensor 204 b. This may occur when although thebiometric sensors 204 a and 204 b use a common lens, the biometricsensors 204 a and 204 b have a different imaging element.

In this case, when the temporal template T_(I′) is generated from animage obtained by the first biometric sensor 104, processes may bestreamlined by sequentially applying the processes. In concrete, first,a temporal template T1 in which a MTF degradation process is applied maybe generated, and the temporal template T1 may be used in anauthentication with use of the biometric sensor 204 a. Sequentially, atemporal template T2 in which a noise adding process is applied to thetemporal template T1 may be generated, and the temporal template T2 maybe used in an authentication with use of the biometric sensor 204 b. Inthis manner, it is possible to streamline the processes more thangenerating each image for each sensor.

Second Embodiment

In the first embodiment, the case where each terminal performs anauthentication process is described. However, an authentication servermay perform the authentication process. For example, a high imagequality sensor is used for entrance to a country, and a low imagequality sensor is used for identity check after the entrance to thecountry. In this case, the authentication server solely performs theauthentication process.

FIG. 12 illustrates a block diagram for describing a hardware structureof a biometric authentication device 400 a in accordance with a secondembodiment. With reference to FIG. 12, the biometric authenticationdevice 400 a has a structure in which a terminal 100 a, a terminal 200a, the storage device 300 and a server 500 are coupled with each othervia a network. The terminal 100 a is, for example, a device performingan authentication of entrance to a country. The terminal 200 a is, forexample, a terminal used for identity check after entrance to thecountry. The server 500 is a sole authentication server that performsauthentication processes.

The terminal 100 a has the CPU 101, the RAM 102, the storage device 103,the first biometric sensor 104, the display device 105, thecommunication device 106 and so on. These components are coupled witheach other via a bus or the like. The terminal 200 a has the CPU 201,the RAM 202, the storage device 203, the second biometric sensor 204,the display device 205, the communication device 206 and so on. Thesecomponents are coupled with each other via a bus or the like. The server500 has a CPU 501, a RAM 502, a storage device 503, a communicationdevice 504 and so on. These components are coupled with each other via abus or the like.

The CPU 501 is a central processing unit. The RAM 502 is a volatilememory temporally storing a program executed by the CPU 501, a dataprocessed by the CPU 501, and so on. The storage device 503 is anonvolatile memory device. The communication devices 504 is an interfacefor transmitting and receiving a signal with an outer component. Thestorage device 300 is a nonvolatile memory device and stores thebiometric authentication program. The biometric authentication programmay be divided into and stored by the storage devices 103. 203 and 503.

Next, a description will be given of each process of the biometricauthentication device 400 a. The biometric authentication program storedin the storage device 300 is developed to the RAMs 102. 202 and 502. TheCPU 101 executes the biometric authentication program developed to theRAM 102. The CPU 201 executes the biometric authentication programdeveloped to the RAM 202. The CPU 501 executes the biometricauthentication program developed to the RAM 502. Thus, each process ofthe biometric authentication device 400 a is performed.

FIG. 13 illustrates a block diagram of each function realized by theexecution of the biometric authentication program. With reference toFIG. 13, by the execution of the biometric authentication program, theterminal 100 a acts as the overall control unit 11, the imaging processunit 12, the authentication process unit 13, the temporal templategeneration unit 15 and the image process unit 16. By the execution ofthe biometric authentication program, the terminal 200 a acts as theoverall control unit 21, the imaging process unit 22 and theauthentication process unit 23. And, by the execution of the biometricauthentication program, the storage device 300 acts as the enrollmentdatabase 30. And, by the execution of the biometric authenticationprogram, the server 500 acts as an overall control unit 31, anauthentication process unit 32, a template obtain unit 33 and a templatecash unit 34.

In the embodiment, the authentication process unit 13 extracts anauthentication feature from a palm image obtained by the biometricsensor 104, and transmits the biometric authentication feature to theserver 500 without performing an authentication process. Theauthentication process unit 23 extracts an authentication feature from apalm image obtained by the second biometric sensor 204 and transmits theauthentication feature to the server 500 without performing anauthentication process.

The overall control unit 31 controls the authentication process unit 32,the template obtain unit 33 and the template cash unit 34. Theauthentication process unit 32 performs an authentication process withuse of the authentication features transmitted from the authenticationprocess unit 13 and the authentication process unit 23 in accordancewith an instruction of the overall control unit 31. The template obtainunit 33 obtains a template from the enrollment database 30 for anauthentication of the authentication process unit 32. The template cashunit 34 temporarily stores a template generated by the temporal templategeneration unit 15.

[Authentication Process]

FIG. 14 illustrates an example of a flowchart executed during anauthentication process with use of the biometric sensor 104. Theauthentication process is performed during entrance to a country or thelike. The imaging process unit 12 obtains an authentication-use palmimage I from the biometric sensor 104 (Step S31). Next, theauthentication process unit 13 extracts an authentication feature F fromthe palm image I (Step S32). Next, the authentication process unit 13transmits the authentication feature F to the server 500 (Step S33).

Next, the authentication process unit 32 compares between theauthentication feature F and an enrolled template T_(R) which thetemplate obtain unit 33 obtains from the enrollment database 30, andcalculates a similarity S of the both (Step S34). Next, theauthentication process unit 32 determines whether the similarity S isequal to or more than the threshold TH₀ (Step S35). When it isdetermined as “Yes” in the Step S35, the authentication process unit 32outputs a signal indicating that the authentication is successful (StepS36). When it is determined as “No” in the Step S35, the authenticationprocess unit 32 outputs a signal indicating that the authentication isfailed (Step S37).

The authentication process unit 13 receives the authentication resultfrom the authentication process unit 32 (Step S38). The authenticationprocess unit 13 determines whether the received authentication resultindicates successful (Step S39). When it is determined as “Yes” in theStep S39, the authentication process unit 13 outputs a signal indicatingthat the authentication is successful (Step S40). Next, the imageprocess unit 16 processes the palm image I and generates an image I′ ofwhich image quality is lower than the image I (Step S41). Next, theauthentication process unit 13 extracts an authentication feature fromthe image I′, and the temporal template generation unit 15 transmits theauthentication feature to the server 500 as a temporal template T_(I′)(Step S42). When it is determined as “No” in the Step S39, theauthentication process unit 13 outputs a signal indicating that theauthentication is failed (Step S43). After the Step S42 or the Step S43,the flowchart of FIG. 14 is terminated.

FIG. 15 illustrates an example of a flowchart executed during anauthentication process with use of the second biometric sensor 204. Theauthentication process is performed after the authentication processwith use of the first biometric sensor 104 is successful, and is, forexample, performed during an identity check after the entrance to thecountry. The imaging process unit 22 obtains an authentication-use palmimage I from the second biometric sensor 204 (Step S51). Next, theauthentication process unit 23 extracts an authentication feature F fromthe palm image I (Step S52). Next, the authentication process unit 23transmits the authentication feature F to the server 500 (Step S53).Next, the authentication process unit 23 receives an authenticationresult from the server 500 (Step S54).

Next, the authentication process unit 23 determines whether the receivedauthentication result is successful (Step S55). When it is determined as“Yes” in the Step S25, the authentication process unit 23 outputs asignal indicating that the authentication is successful (Step S56). Whenit is determined as “No” in the Step S55, the authentication processunit 23 outputs a signal indicating that the authentication is failed(Step S57). After the Step S56 or the Step S57, the flowchart of FIG. 15is terminated.

FIG. 16 illustrates an example of a flowchart executed by the server 500after the Step S53 of FIG. 15. With reference to FIG. 16, theauthentication process unit 32 receives an authentication feature F fromthe authentication process unit 23 (Step S61). Next, the authenticationprocess unit 32 compares between the authentication feature F and anenrolled template T_(R) which the template obtain unit 33 obtains fromthe enrollment database 30, and calculates a similarity of the both(Step S62).

Next, the authentication process unit 32 determines whether thesimilarity S is equal to or more than a threshold TH₁ (Step S63). Whenit is determined as “No” in the Step S63, the authentication processunit 32 determines whether the similarity S is equal to or more than athreshold TH₂ (<TH₁) (Step S64). When it is determined as “Yes” in theStep S64, the template obtain unit 33 obtains a temporal template T_(I′)from the template cash unit 34 (Step S65).

Next, the authentication process unit compares the authenticationfeature F and the temporal template T₁ and calculates a similarity S′ ofthe both (Step S66). Next, the authentication process unit 32 determineswhether the similarity S′ is equal to or more than a threshold TH₃ (StepS67). When it is determined as “Yes” in the Step S67 or it is determinedas “Yes” in the Step S64, the authentication process unit 32 returns asignal indicating that the authentication is successful to the terminal200 a (Step S68). When it is determined as “No” in the Step S64 or whenit is determined as “No” in the Step S67, the authentication processunit 32 returns a signal indicating that the authentication is failed tothe terminal 200 a (Step S69). After the Step S19 or the Step S20, theexecution of the flowchart of FIG. 15 is terminated.

In the embodiment, it is possible to use biometric information allowingsuccessful of an authentication obtained by the first biometric sensor104 of which reproducibility is high during an authentication based onbiometric information obtained by the second biometric sensor 204 ofwhich reproducibility is low. Therefore, biometric information havinghigh reliability can be used. Accordingly, it is possible to suppressdegradation of authentication accuracy with use of the second biometricsensor 204. And, degradation of convenience may be suppressed. Highreproducibility is not required for the second biometric sensor 204because the biometric information having high reliability can be used.Therefore, an inexpensive device can be used as the second biometricsensor 204. And, the cost can be suppressed.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various change, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

What is claimed is:
 1. A biometric authentication device comprising: afirst biometric sensor that obtains biometric information of a user; asecond biometric sensor that obtains biometric information of a user ata lower degree of reproducibility than the first biometric sensor; anauthentication process unit that performs an authentication by comparingwith use of the biometric information obtained by the first biometricsensor and the second biometric sensor, wherein the authenticationprocess unit compares biometric information obtained by the secondbiometric sensor with use of biometric information obtained by the firstbiometric sensor of a case where a comparing between the biometricinformation obtained by the first biometric sensor and enrolledinformation is successful.
 2. The biometric authentication device asclaimed in claim 1 further comprising: a process unit that processes thebiometric information obtained by the first biometric sensor of the casewhere the comparing between the biometric information and the enrolledinformation is successful, wherein the authentication process unitperforms an authentication by comparing a processed biometricinformation processed by the process unit and the biometric informationobtained by the second biometric sensor.
 3. The biometric authenticationdevice as claimed in claim 2, wherein the authentication process unitperforms an authentication by comparing the processed biometricinformation and the biometric information obtained by the secondbiometric sensor when the comparing between the biometric informationobtained by the second biometric sensor and the enrolled information isfailed.
 4. The biometric authentication device as claimed in claim 2,wherein: the first biometric sensor and the second biometric sensor aresensors that obtain a biometric image; and the process unit performs aprocess of lowering image quality of the biometric image obtained by thefirst biometric sensor.
 5. The biometric authentication device asclaimed in claim 1, wherein the authentication process unit reflects aresult of the comparing between the biometric information obtained bythe second biometric sensor and the enrolled information to thecomparing between the biometric information obtained by the secondbiometric sensor and the biometric information obtained by the firstbiometric sensor of the case where the comparing between the biometricinformation obtained by the first biometric sensor and the enrolledinformation is successful.
 6. A biometric authentication methodcomprising: performing an authentication by comparing biometricinformation obtained by a first biometric sensor that obtains biometricinformation of a user and an enrolled information; and with use of thebiometric information of a case where the comparing is successful,performing an authentication by comparing biometric information obtainedby a second biometric sensor that obtains biometric information of auser at a lower degree of reproducibility than the first biometricsensor.
 7. A computer readable, non-transitory medium storing a programthat causes a computer to execute a process, the process comprising:performing an authentication by comparing biometric information obtainedby a first biometric sensor that obtains biometric information of a userand an enrolled information; and with use of the biometric informationof a case where the comparing is successful, performing anauthentication by comparing biometric information obtained by a secondbiometric sensor that obtains biometric information of a user at a lowerdegree of reproducibility than the first biometric sensor.